1. Field of the Invention
The invention relates generally to arc lamps and specifically to devices and methods used to cool the anode electrode of arc lamps.
2. Description of the Prior Art
Short arc lamps provide intense point sources of light that allow light collection in reflectors for applications in medical endoscopes, instrumentation and projection. Also, short arc lamps are used in industrial endoscopes, for example in the inspection of jet engine interiors.
A typical short arc lamp comprises an anode and a cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains a gas pressurized to several atmospheres. U.S. Pat. 4,633,128, issued Dec. 30, 1986, to Roy D. Roberts, the present inventor, and Robert L. Miner, describes such a short arc lamp in which a copper sleeve member is attached to the reflecting wall to conduct heat from the reflecting wall through to the exterior wall and eventually to circulating ambient air.
The lamp illustrated in FIG. 2 of Roberts, et al., can be operated at one kilowatt. At higher power levels, the heat generated by an electric arc between cathode 42 and anode 44 encounters thermal resistance to the ambient which may result in overheating and potential failure. Specifically, applying too much power to the lamp creates thermal gradients in the ceramic material that may cause cracks in the body and possibly an explosion of a weakened lamp.
Conventional short arc lamps have solid anodes that tend to get very hot at the center of the face supporting the arc. A portion of the electrode metal usually vaporizes and then deposits on the reflector. These deposits blacken the reflector and cause increased heat absorption. As a result, lamp life is seriously curtailed by such deposits.